The proposed project is an exploratory study of the possible physiological implications for liver regeneration of the interactions of ethanol with growth factor-induced signal transduction processes. Ethanol has been reported to inhibit liver regeneration after partial hepatectomy in vivo. Also, liver regeneration is deficient in chronically ethanol-fed animals. Our preliminary studies indicated that ethanol inhibits the activation of phospholipase C induced by epidermal growth factor (EGF) in isolated hepatocytes; furthermore, ethanol inhibits EGF-induced DNA syntheses in hepatocytes in primary culture. The effects of ethanol on the early signal transduction processes induced by EGF and other growth factors acting on hepatocytes will be investigated. The role of receptor availability, tyrosine kinase activity, activation of phospholipase C and phospholipase d, changes in cellular levels of inositol phosphate diacylglycerol and phosphatidic acid, and the pattern of Ca2+-mobilization will be studied. The role of protein kinase A and protein kinase C in the control of EGF-induced signalling processes and its sensitivity to ethanol will be investigated using specific activators and inhibitors of these processes. The effect of ethanol on EGF receptor density and on the rate of receptor internalization will be studied. The effect of ethanol on signal transduction mechanisms of other growth factors acting on liver will be analyzed; specifically, the second messenger responses to hepatocyte growth factor-mediated signal transduction processes will be correlated with its effects on the growth factor-induced stimulation of DNA synthesis. These studies on isolated hepatocytes will be complemented by an analysis of the effects of ethanol on second messenger patterns associated with liver regeneration after partial hepotectomy. The effects of long-term ethanol exposure on the responsiveness to growth factor will be studied both in vitro, in a model system with cultured hepatocytes, and in vivo, after chronic ethanol feeding of the animal. These studies are expected to expand our understanding of the interactions of ethanol with the mechanism of action of growth hormones in liver cells which relate to the effects of ethanol on the control of liver regeneration.